DESCRIPTION: Dopamine (DA) neurons in the substantia nigra pars compacta (SNc) play a crucial role in basal- ganglia mediated motor function. Indeed loss of SNc DA neurons leads to the motor deficits in Parkinson's disease. However, the role of these neurons in the normal control of movement is poorly understood. Eventual understanding of mechanisms underlying Parkinson's disease and development of treatment strategies largely depends on understanding DA neuron properties. One of the most critical mechanisms that controls neuronal firing pattern is the prolonged afterhyperpolarization (AHP) that follows a single action potential or burst of action potentials. In DA neurons the AHP contributes to the regulation of the frequency and pattern of spontaneous and evoked discharges and is mediated in part by apamin-sensitive Ca2+-activated K+ channels. In addition, however, an apamin-insensitive component is mediated by an as yet unidentified Ca2+- insensitive channel. Our previous studies showed that membrane properties and firing frequency of DA neurons in the SNc are modulated by endogenous hydrogen peroxide (H2O2) and this modulation occurs via ATP-sensitive K+ (KATP) channels. In DA neurons burst-like firing induced by depolarizing current injection is accompanied by an increase in the production of reactive oxygen species, like H2O2, as well as a prolonged AHP. Excitingly, new data presented in this application shows that the H2O2-metabolyzing enzyme, catalase, and the selective KATP channel blocker, glibenclamide, significantly decrease the amplitude and duration of the AHP in DA neurons, suggesting an involvement of both H2O2 and KATP channels. Proposed studies will therefore test the involvement of these factors in the AHP in DA neurons. I will use patch-clamp recording coupled with fluorescence imaging of H2O2 in SNc DA neurons in guinea pig midbrain slices. Current-clamp mode will be used to study AHP amplitude and duration and hybrid-clamp recording to assess the AHP tail current. Experiments in Aim 1 will address the question whether the AHP in DA neurons has an H2O2- sensitive component and assess its sensitivity to apamin. The involvement of H2O2-sensitive KATP channels in the AHP in SNc DA neuron will be assessed in Aim 2. Overall, this project will provide unique insights into dynamic regulation of AHP and consequently DA neuron activity by H2O2 and KATP channels. PUBLIC HEALTH RELEVANCE This project is focused on testing a novel hypothesis concerning the regulation of the activity of dopaminergic neurons in the substantia nigra pars compacta (SNc). These cells play a crucial role in basal ganglia mediated function. Indeed loss of SNc dopamine neurons leads to motor deficits in Parkinson's disease. This study could therefore potentially lead to the development of novel antiparkinsonian drugs. Thus, it is of direct relevance to NINDS which supports projects focused on the discovery of mechanisms of neurodegenerative disorders.